Reject method comparison
Start with the product and the reject window.
The same mechanism will not suit every line. A rigid carton may tolerate a positive side push, while an unstable pouch may need a fast air jet or controlled downward route. A fragile product may require support for longer, and a large case may need redirection rather than a sharp impact.
The reject window is the time and space available to remove one failed product without touching the products before or after it. It is affected by belt speed, product length, minimum gap, actuator travel, recovery time and the distance needed for the product to clear the accepted flow.
| Reject method | Often considered for | Key strengths | Important checks |
|---|---|---|---|
| Pneumatic pusher | Stable cartons, bottles, tubs and trays | Positive, controlled side ejection | Product stability, gap, stroke, side clearance and air supply |
| Air blast | Lightweight packs, sachets and small products | Fast action with no arm entering the flow | Product mass, air consumption, noise and controlled flight path |
| Drop flap | Small packs with a suitable downward route | Compact, positive separation below the line | Product support, flap cycle, gap and collection clearance |
| Retracting belt | Fragile, awkward or closely controlled products | Supported product handling and downward transfer | Retraction distance, cycle time, transfer geometry and belt control |
| Swing-arm diverter | Larger packs, cases, rework and lane routing | Positive redirection into another conveyor route | Product footprint, guide length, route space and downstream capacity |
| Lane divert | Products requiring classification or alternate lanes | Controlled sorting rather than bin rejection | Lane geometry, tracking, accumulation and destination capacity |
Seven questions that define the application
1. What is the product?
Record minimum and maximum dimensions, weight, centre of gravity, rigidity, surface, orientation and anything that makes it unstable or fragile.
2. How fast is the line?
Use actual belt speed, throughput and minimum product pitch. Average production rate alone does not define the shortest reject window.
3. What triggers rejection?
Identify the checkweigher, metal detector, vision system, X-ray system or other line control and its output signals.
4. Where can the reject happen?
Measure usable conveyor length, width, height, side clearance, floor space, guarding envelope and access for operation, cleaning and maintenance.
5. Where does failed product go?
Define bin size, guarding, lockable access, reject frequency, full-bin response and the procedure for removing or investigating rejected items.
6. How is removal proved?
Decide whether the process needs independent reject confirmation, actuator monitoring, bin sensing or audit signals.
7. What happens on a fault?
Agree the response to missing confirmation, loss of air, missing bin, open access, sensor fault or unavailable downstream capacity.
Retrofit checklist for an existing line
For an existing conveyor, provide a dimensioned layout, photographs from both sides, a short production video, belt width and height, speed range, product pitch, electrical supply, compressed-air availability and the inspection equipment manual or interface details. Also identify operator routes and any access that must remain clear.
A retrofit review must consider whether the existing belt and frame can maintain product control, whether there is enough tracking and reject distance, and how the new equipment will interface with current guarding and line controls. If those constraints are unsuitable, a replacement conveyor section may create a more dependable solution.
Acceptance testing: prove the operating window
Testing should cover representative minimum and maximum products, normal and maximum speed, shortest expected pitch, repeat reject events and the agreed fault scenarios. Good products should remain stable while failed products clear the accepted flow and enter the controlled reject route.
Where reject verification is specified, testing should also show that the expected confirmation is received and that a deliberately missing confirmation produces the defined alarm or stop response. Documented challenge tests give operators a repeatable way to check the reject path after installation.
Reject conveyor selection FAQs
What is the best reject mechanism for packaged products?+
There is no single best mechanism. Stable rigid packs often suit pushers, light products may suit air blast, fragile or awkward products may need a retracting belt, small packs can suit a drop flap, and larger cases may suit a diverter.
How much product gap does a reject conveyor need?+
The required gap depends on reject-device movement, product dimensions, belt speed and the time needed to separate one failed pack without disturbing its neighbours. It must be calculated and then confirmed by product testing.
What does fail-safe rejection mean?+
Fail-safe rejection means the system monitors the conditions needed for dependable removal and enters an agreed alarm or stop state when rejection is not confirmed or a critical condition is unavailable.
Can an automatic reject system be added to an existing conveyor?+
Often, yes. Suitability depends on available length, belt and frame condition, product control, inspection signals, sensor positions, guarding, reject containment and the required line-control interface.